A qualitative PCR minipool strategy to screen for virologic failure and antiretroviral drug resistance in South African patients on first-line antiretroviral therapy.

BACKGROUND

The high cost of commercial HIV-1 viral load tests for monitoring of patients on antiretroviral treatment limits their use in resource-constrained settings. Commercial genotypic antiretroviral resistance testing is even more costly, yet it provides important benefits.

OBJECTIVES

We sought to determine the sensitivity and negative predictive value of a qualitative PCR targeting partial reverse transcriptase for detection of virologic failure when 5 patient specimens are pooled.

STUDY DESIGN

A total of 300 South African routine patient samples were included and tested in 60 pools of 5 samples each. A qualitative nested PCR was optimised for testing pools and individual samples from positive pools. All positive samples were sequenced to detect drug resistance-associated mutations. Results were compared to those of conventional viral load monitoring.

RESULTS

Twenty-two of 60 pools tested positive. Individual testing yielded 29 positive individual samples. Twenty-six patients had viral loads of above 1000 copies/ml. The pooling algorithm detected 24 of those 26 patients, resulting in a negative predictive value of 99.3%, and a positive predictive value of 89.7%. The sensitivity for detecting patients failing therapy was 92%, with a specificity of 98.9%. Of the patients failing first-line ART, 83.3% had NRTI and 91.7% NNRTI resistance mutations.

CONCLUSIONS

The pooled testing algorithm presented here required 43% fewer assays than conventional viral load testing. In addition to offering a potential cost saving over individual viral load testing, it also provided drug resistance information which is not available routinely in resourced-limited settings.